The invention relates to a semiconductor device and a method for fabricating the same, and especially to a semiconductor device in which a semiconductor chip is assembled into a printed circuit board and a method for fabricating the same.
In recent years, an electronic device has come to be integrated with high density, and a semiconductor chip with multiple terminals is packaged in accordance with an improvement of the function and thinning of an electronic circuit. Accordingly, a package of the semiconductor chip used in the electronic circuit is miniaturized and provided with multiple pins. In conformity with the aforementioned tendency, the semiconductor chip is assembled into a printed circuit board by means of a package of an area array type, such as a ball grid array package (BGA), a chip scale package (CSP) or a bare chip package (a flip chip package, FC).
FIG. 1 shows a typical example of the structure of the aforementioned packages of the semiconductor chips. In the package shown in FIG. 1, a chip-mounting substrate 103 on which a semiconductor chip 100 has been mounted by means of wire-bonding is assembled into a printed circuit board 104 by CSP, where the chip-mounting substrate 103 is composed of an insulating substrate 101 formed of ceramics, polyimide, etc. and conductor wirings 102.
In the package having the aforementioned structure, a clearance formed between the chip-mounting substrate 103 and the printed circuit board 104 is filled with underfill material 105 in order to absorb a stress caused by a difference in the thermal expansion coefficient between the chip-mounting substrate 103 and the printed circuit board 104 and impacts caused by fallings to secure the reliability of soldered jointed portions.
However, if alien substances mix with underfill material 105 or the impacts exert on under fill material 105 for a long period of time, an adhesive strength of underfill material 105 is lowered, and underfill material 105 may exfoliate form the surface of the chip-mounting substrate 103 or of the printed circuit board 104.
If underfill material 105 exfoliates from the chip-mounting substrate 103 or the printed circuit board 104, since the stress concentrates on joined portions of the solder balls 106, cracks occur on pads 107, 108 which are respectively formed on surfaces of the chip-mounting substrate 103 and the printed circuit board 104, and the joined portions become disincentive. As mentioned in the above, the reliability of the semiconductor device is lowered because of lowering of the adhesive strength of underfill material 105.
In Japanese Patent Applications, Laid-Open, No.63-94646, an electronic device in which unevennesses are respectively provided for a predetermined part of a chip-mounting substrate and sealing resin for sealing a semiconductor chip is disclosed as a means for increasing an adhesive strength between the chip-mounting substrate and the basic substrate. That is to say, in the aforementioned semiconductor device, concave portions and convex portions are alternately formed on the chip-mounting substrate and on sealing resin for covering the semiconductor chip, and the chip-mounting substrate on which the semiconductor chip is mounted is buried in a cavity formed in the basic substrate. Accordingly, the aforementioned technology cannot be applied to a package of an area array type.
Although a semiconductor device in which a bonding wire is prevented from being disincentive by providing unevenness for a pad is disclosed in Japanese Patent No.2973988, underfill material is not prevented from being exfoliated according to this technology.
In a semiconductor device in which a semiconductor chip mounted on a lead frame is assembled into a printed circuit board, since there is a difference in a thermal expansion coefficient between the lead frame and a pad of the printed circuit board, the lead frame may exfoliate from the printed circuit board at a contact surface therebetween because of an impact caused by a thermal shock.
Accordingly, it is an object of the invention to provide a semiconductor device in which a chip-mounting substrate or a lead frame adheres to a printed circuit board tightly, and a method for fabricating the same.
It is a further object of the invention to provide a semiconductor device operating in an electronic circuit with high reliability, and a method for fabricating the same.
A semiconductor device concerned with the first viewpoint of the invention comprises:
a semiconductor chip,
a chip-mounting substrate which is provided with the semiconductor chip mounted on a top surface thereof and the first conductive pads formed on a bottom surface thereof and connected with the semiconductor chip electrically,
solder balls formed on the first conductive pads,
a printed circuit board on which second conductive pads connected with the solder balls are formed, and
underfill material injected into a clearance formed between the chip-mounting substrate and the printed circuit board,
wherein unevenness is formed on a surface which is brought into contact with the underfill material of at least one of the chip-mounting substrate and the printed circuit board.
According to the aforementioned structure, since an area of a contact surface between the chip-mounting substrate and underfill material increases, an adhesive strength between the chip-mounting substrate and underfill material is heightened. Accordingly, the chip-mounting substrate becomes hard to exfoliate from underfill material, and an adhesive strength between the chip-mounting substrate and the printed circuit board is heightened. Moreover, since the adhesive strength between the chip-mounting substrate and the printed circuit board is heightened, a disconnection between the solder ball and the pad becomes hard to occur. Accordingly, the semiconductor device operating in the electronic circuit with high reliability can be obtained.
The aforementioned unevenness may be selectively formed on the first conductive pads or on the second conductive pads.
Moreover, the aforementioned unevenness may be shaped into a slit-like configuration or into a dimple-like configuration.
A semiconductor device concerned with the second view point of the invention comprises:
a semiconductor chip,
a lead frame which is provided with the semiconductor chip mounted thereon and electrically connected with the semiconductor chip, and
a printed circuit board including the third conductive pads which are formed thereon and brought into contact with the lead frame,
wherein at least one of the lead frame and the printed circuit board is provided with unevennesses at contact surfaces therebetween.
According to the aforementioned structure, since an area of a contact surface between the lead frame and the printed circuit board increases, the lead frame becomes hard to exfoliate from the printed circuit board, and the adhesive strength between the lead frame and the printed circuit board is heightened. Moreover, since the adhesive strength between the lead frame and the printed circuit board is heightened, a jointed portion between the lead frame and the printed circuit board becomes hard to be disincentive. Accordingly, the semiconductor device operating in the electronic circuit with high reliability can be obtained.
A method for fabricating a semiconductor device concerned with the third viewpoint of the invention comprises the steps of:
forming the fourth conductive pads on a bottom surface of a chip-mounting substrate,
forming unevenness on the bottom surface of the chip-mounting substrate,
mounting a semiconductor chip on a top surface of the chip-mounting substrate,
connecting the semiconductor chip with the fourth conductive pads electrically,
forming solder balls on the fourth conductive pads,
assembling the chip-mounting substrate into a printed circuit board by connecting solder balls with the fifth conductive pads formed on the printed circuit board, and
injecting underfill material into a clearance formed between the chip-mounting substrate and the printed circuit board.
According to the aforementioned structure, since an area of a contact surface between the chip-mounting substrate and underfill material increases, the adhesive strength between the chip-mounting substrate and underfill material is heightened. Accordingly, the chip-mounting substrate becomes hard to exfoliate from underfill material, and the adhesive strength between the chip-mounting substrate and the printed circuit board is heightened. Moreover, since the adhesive strength between the chip-mounting substrate and the printed circuit is heightened, a disconnection between the solder ball and the pad becomes hard to occur. Accordingly, the semiconductor device operating in the electronic circuit with high reliability can be obtained.
The aforementioned step of forming unevenness on the bottom surface of the chip mounting substrate may comprise the step of forming unevennesses on the fourth conductive pads.
A method for fabricating the semiconductor device concerned with the fourth view point of the invention comprises the steps of:
forming the sixth conductive pads on a bottom surface of a chip-mounting substrate,
mounting a semiconductor chip on a top surface of the chip-mounting substrate,
connecting the semiconductor chip with the sixth conductive pads electrically,
forming solder balls on the sixth conductive pads,
forming unevenness on a surface of a printed circuit board on which the seventh conductive pads are formed,
assembling the chip-mounting substrate into the printed circuit board by connecting the solder balls with the seventh conductive pads formed on the printed circuit board, and
injected underfill material into a clearance formed between the chip-mounting substrate and the printed circuit board.
According to the aforementioned structure, since an area of the contact surface between the printed circuit board and underfill material increases, the adhesive strength between the printed circuit board and underfill material is heightened. Accordingly, underfill material becomes hard to exfoliate from the printed circuit board, and the adhesive strength between the chip-mounting substrate and the printed circuit board is heightened. Moreover, since the adhesive strength between the chip-mounting substrate and the printed circuit board is heightened, a disconnection between the solder ball and the pad becomes hard to occur. Accordingly, the semiconductor device operating in the electronic circuit with high reliability can be obtained.
The step of forming unevenness on the surface of the printed circuit board may comprise the step of forming unevennesses on the surfaces of the seventh conductive pads selectively.
A method for fabrication a semiconductor device concerned with the fifth view point of the invention comprises the steps of:
forming the eighth conductive pads on a bottom surface of a chip-mounting substrate,
forming the first unevenness on a bottom surface of the chip-mounting substrate,
mounting a semiconductor chip on a top surface of the chip-mounting substrate,
connecting the semiconductor chip with the eighth conductive pads electrically,
forming solder balls on the eighth conductive pads,
forming the second unevenness on a surface of a printed circuit board on which the ninth conductive pads are formed,
assembling the chip-mounting substrate into the printed circuit board by connecting the solder balls with the ninth conductive pads, and
injecting underfill material into a clearance formed between the chip-mooting substrate and the printed circuit board.
According to the aforementioned structure, since an area of a contact surface between the chip-mounting substrate and underfill material increases, the adhesive strength therebetween is heightened. Similarly, since an area of a contact surface between the printed circuit board and underfill material increases, the adhesive strength therebetween is heightened also. Accordingly, underfill material becomes hard to exfoliate from both the chip-mounting substrate and the printed circuit board, and the adhesive strength between the chip-mounting substrate and the printed circuit board is heightened. Moreover, since the adhesive strength between the chip-mounting substrate and the printed circuit board is heightened, a disconnection between the solder ball and the pad becomes hard to occur. As a result, the semiconductor device operating in the electronic circuit with high reliability can be obtained.
The step of forming unevenness on the bottom surface of the chip-mounting substrate may comprise the step of forming unevennesses on the surfaces of the eighth conductive pads selectively, and
The step of forming unevenness on the top surface of the printed circuit board may comprise the step of forming unevennesses on the surfaces of the ninth conductive pads selectively.
A method for fabricating a semiconductor device concerning with the sixth view point of the invention comprises the steps of:
forming unevennesses on predetermined parts of a lead frame,
mounting a semiconductor chip on the lead frame,
connecting the semiconductor chip with the lead frame electrically, and
assembling the lead frame on which the semiconductor chip is mounted into a printed circuit board by bringing the unevennesses formed on the lead frame into contact with tenth conductive pads formed on the printed circuit board.
According to the aforementioned structure, since areas of the contact surfaces between the lead frame and the printed circuit board increase, the lead frame becomes hard to exfoliate from the printed circuit board, and the adhesive strength between the lead frame and the printed circuit board is heightened. Moreover, since the adhesive strength between the lead frame and the printed circuit board is heightened, a disconnection of a jointed portion between the lead frame and the printed circuit board becomes hard to occur. Accordingly, the semiconductor device operating with high reliability n the electronic circuit can be obtained.
A method for fabricating a semiconductor device concerned with the seventh view point of the invention comprises the steps of:
mounting a semiconductor chip on a lead frame,
forming unevennesses on surfaces of eleventh conductive pads formed on a printed circuit board, and
assembling the lead frame on which the semiconductor chip is mounted into the printed circuit board by connecting the lead frame with the eleventh conductive pads on which the unevennesses are formed.
A method for fabricating a semiconductor device concerned with the eighth viewpoint of the invention comprises the steps of:
forming the first unevennesses on predetermined parts of a lead frame,
mounting a semiconductor chip on the lead frame,
connecting the semiconductor chip with the lead frame electrically,
forming the second unevennesses on surfaces of twelfth conductive pads formed on a printed circuit board, and
assembling the lead frame on which the semiconductor chip is mounted into the printed circuit board by bringing the first unevennesses formed on the lead frame into contact with the second unevennesses formed on the twelfth conductive pads.